A map based on the research of Priscilla W. McNeill shows the patchwork of tracts along the Potomac and the “Eastern Branch” — now the Anacostia — before the District was established. (Courtesy of Cynthia Elliott)

In the beginning, before Washington was Washington, before the White House, the Capitol and the monuments, maps show almost nothing along the Potomac River between Rock Creek and the Anacostia.

There was Notley Young’s plantation, with its brick mansion, graveyards and slave quarters. There was a village called Hamburg that existed only on paper. The capital was then a few thousand acres of empty upland and wetlands with a smattering of residents along a broad, mostly placid river.

Next week, the Library of Congress hosts what it says is the first conference on the mapping of Washington — a look at how cartographers sketched in the blank canvas along the “Potomack” and filled out the portrait over the next two centuries.

It is the story of an invented city, a “paper city,” on a site picked by George Washington, following a design by the French-born architect and veteran of Valley Forge Pierre Charles L’Enfant, with tweaks by Thomas Jefferson.

“No nation perhaps had ever before the opportunity . . . of deliberately deciding on the spot where their Capital city should be fixed,” L’Enfant wrote Washington in 1789. Like the new country, the city would be fresh and innovative, a work of science and art.

The library’s world-class map collection details the evolution of the “Territory of Columbia” from L’Enfant’s radiating hubs to the arrival on Jenkins Heights of the solitary Capitol (with a fence to keep the cows out) to the city’s advancement beyond Boundary — now Florida — Avenue.

Along the way, the maps, which library officials recently previewed, show that plans changed.

Goose Creek was renamed Tiber Creek, turned into a canal and then buried beneath Constitution Avenue. “Congress House” became the Capitol. And what was the “Eastern Branch” of the Potomac River became the Anacostia.

The “grand cascade” on Capitol Hill was never realized, nor was the national church downtown or the commercial center on East Capitol Street. There was a Mall, but it ended at the river bank, then just south of the White House.

In 1790, Congress decided to locate the capital somewhere along an 80-mile stretch of the Potomac but left it to President George Washington to pick the exact site. He did so a year later, choosing a spot between the ports of “George Town” and Alexandria.

Washington “believed that a successful capital city . . . was a necessity because . . . the Constitution was paper and changeable,” said Don Alexander Hawkins, a Washington architect and longtime student of the city’s design. “He felt that continuity was important and that the capital city would demonstrate the value of the Constitution.”

By 1800, when the government moved here, there were only 372 houses and 3,000 residents.

Map shows the site one of the few structures that existed before Washington was built. (Gene Thorp/Library of Congress)

By the Civil War, though, the maps indicate a population of 61,000 in a Washington ringed by so many forts that it was “the most fortified city in America, and probably in the world,” said Ralph E. Ehrenberg, chief of the library’s geography and map division.

There are topographical maps, old fire insurance maps — the Treasury Department is labeled a “war risk” building — and old school precinct maps, which have one category for white schools and another for “colored.”

There’s an 1883 commercial map that shows a brewery where the Kennedy Center is now, another that shows the long-vanished “Babcock lakes” at the Washington Monument, and others that show the Potomac River “reclamation” area, soon to become the west end of the Mall.

There are color-coded statistical maps from the late 1800s showing the city’s gas lamps, telegraph lines and paved streets. One shows the frequency of street sweeping. Pennsylvania Avenue near the White House was swept every day.

Many maps of that era depict factories belching smoke. “Smoke reflects industry,” Ehrenberg said, “and that was good in America. We honored industry at one time.”

A colorful map shows the city’s pitch to host the World’s Exposition of 1892, with sites around the Washington Monument for a national zoo, a statue of Columbus and a hall of invention models. But the pitch failed, and the exposition went to Chicago.

Perhaps the most interesting maps are those that show what the area was like before the city was born. One newer map, researched by Priscilla W. McNeill and published in 1991, depicts tracts like Widow’s Mite in what is today Foggy Bottom, Flint’s Discovery, northeast of Dupont Circle, and Hamburg, north of what is now the Mall’s Constitution Gardens.

Notley Young’s plantation was along the water in the area of what today is Maine Avenue SW.

A map dating from the late 1700s depicts the footprints of the riverfront mansion, two graveyards, the “overseers garden” and an 11-structure complex designated “houses occupied by negro’s.”

One of the presenters at the conference, Dan Bailey, director of the Imaging Research Center at the University of Maryland Baltimore County, has built a high-tech visual re-creation of Young’s vanished spread.

Walking in the footsteps of the old map makers, Bailey said: “We picked Notley Young’s plantation for a variety of reasons. . . . He was a major slaveholder. . . . He was also Catholic.”

Bailey said his team studied the map, talked to experts and researched local history. “We [virtually] rebuilt the buildings,” he said. “We positioned the buildings in space. One of the maps gave us clues as to where gardens were, where tobacco fields were.”

The conclusion, he said, was that this was “a pretty classic plantation, with the long driveway coming up, trees on both sides.”

Indeed, a 1912 presentation before the District’s old Columbia Historical Society by a former resident of the mansion, George C. Henning, paints just such a picture.

Henning, who had lived there as a child in the late 1830s, described the locust trees along the river bank and the yellow jasmine that grew north of the house, which had a pillared front porch.

Young died in 1802. His house was demolished in 1856. But his plantation lives on in the virtual universe, and a map vault in the Library of Congress.

The conference, titled “Visualizing the Nation’s Capital,” runs Friday and Saturday. It’s free and open to the public, but reservations are required. They can be made at specialevents@ loc.gov or by calling 202-707-1616.